Research Technical Report

Recovery of Rocky Intertidal Assemblages Following the Wreck and Salvage of the F/V Trinity. Final Report: Years 1 and 2 (April 1996-May 1998).

Walder, R.K., and M.S. Foster (June 2000)

MBNMS Technical Report, 52pp.

SUMMARY

The grounding and subsequent salvage of the F/V Trinity, a 51 foot, steel hull seiner, at Point Pinos, on the Monterey Peninsula on April, 20 1996 resulted in a total of 251 m2 of physical damage and 287 m2 of chemical damage to the rocky intertidal habitat. As a part of the Monterey Bay National Marine Sanctuary Intertidal Monitoring Program, biological damage and recovery are being investigated to understand the recovery process. A potential restoration technique is also being tested to enhance recovery. This report presents results of these studies from April 1996 to May 1998.

Physical damage, caused by crushing and scraping, exposed fresh vertical and horizontal surfaces removed some of the macroflora and macrofauna. Two rubble beds (one in the mid and one in the low intertidal) were also formed where the vessel crushed boulders into small pieces. A pit was formed (in the mid/high intertidal) in the sand by two large tires used to cushion the vessel. Spilled diesel fuel and possibly hydraulic fluid and engine oil likely caused surf grass bleaching and blade loss. More research is needed to further understand the human induced and natural bleaching phenomena in plant assemblages.

Recovery on newly exposed, horizontal surfaces within three assemblages (low intertidal surf grass, mid intertidal mussel, and mid/high intertidal red algae) are being quantitatively assessed. Plots were established in the disturbed areas, adjacent intact assemblages (wreck controls) and intact assemblages outside of the potential chemical spill area (spill controls). The spill controls were considered the undisturbed natural condition for an assemblage unless no significant difference could be found between the spill controls and the wreck controls. If no difference was detected, the survey of spill controls was discontinued and the wreck controls were considered the undisturbed natural condition for comparison. Recovery of rubble beds, newly exposed vertical rock surfaces and a sand pit were qualitatively assessed. To examine the feasibility of using transplanted boulders with intact assemblages as a restoration technique to enhance recovery of damage habitats, nine small (15-30 cm) and nine large (40-60 cm) boulders were transplanted to a rubble bed. Survival and reproductive condition of species on boulders was qualitatively assessed.

Recovery within damaged plots has been slow. After six surveys (June, August and December of 1996; May and December of 1997 and May 1998) some of the species that dominate each natural assemblage have colonized. Prior studies in these assemblages noted variable recovery with predictions of recovery ranging "from one to more than six years" for the red algal assemblage to "probably greater than 10 years" for the mussel assemblage (Kinnetic Laboratories Inc., 1992). Some studies have suggested colonization of open space is more rapid on the lower shore. Colonization of disturbed plots in the low intertidal surfgrass assemblage has been most rapid while that in the mid/high intertidal red algal assemblage has been the least.

Algal recruitment is occurring in the two rubble beds. One of these beds, located in the mid intertidal, is being colonized slowly, probably because continued disturbance from loose rubble is limiting successful recruitment. High wave action will eventually wash the loose rubble from the bed exposing the stable surface beneath which is more suitable for colonization. Recruitment in the low intertidal rubble bed has been more rapid, possibly because smaller rocks were washed out of the bed and colonization is more rapid. A low intertidal vertical rock face, exposed by fracture during the wreck, appears to be recovering more rapidly than any other disturbed habitat, perhaps because it is a stable, low intertidal surface. Since its formation, sand has shifted in and out of the sand pit with high wave action suggesting that initial damage from the wreck was minimal. Nevertheless, to minimize damage, it would be better to remove equipment while it is not being used for salvage operations. As of the May 1998 survey, 15 of 18 transplanted boulders remained. The results suggest that future transplants be done with large boulders since the initial survival of the dominant species was greater on them. However, transplants should not be placed in an area where they are subject to sand and rock scour. Present funds maintained this project through May 1998 and potential exists for using future mitigation funds to support the study until recovery occurs.